Is heart meat lean enough for pemmican?

I'd like to try making pemmican, but you need really lean meat and the best bang for the buck is heart meat - I think. It has no fatty marbling. Trim the fat deposits off the outside, and it seems as lean as lean can be.

However, it's much juicier and tendered that typical lean cuts. (Tastier too, if you ask me.) So maybe there's a lot of hidden fat.

Can anyone tell me if it's lean enough, or should I go buy some yucky eye of round or something?